In a UMTS Terrestrial Radio Access Network (UTRAN) or an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), cells of different coverage sizes are deployed to improve cell coverage or to offload traffic. In a UTRAN or E-UTRAN network, small cells (e.g., pico cells, relay cells, or femto cells) are deployed with overlaid large cells (e.g., macro cells). A network including large cells and small cells is referred to as a heterogeneous wireless communication network or, for simplicity, as a heterogeneous network.
Macro cells and small cells may operate in the same carrier frequency or different carrier frequencies. For example, in a heterogeneous network consisting of macro cells and pico cells, the macro cells may operate on one carrier frequency while the pico cells may operate on another carrier frequency. Operating the macro cells and pico cells on different carrier frequencies helps to reduce the interference among cells. A user equipment (UE) in the heterogeneous network may move in a large geographical area which may result in changing of the UE's serving cell and the cell type (e.g., macro cell, pico cell, relay cell, femto cell) of the UE's serving cell.